Effect of a 6-week weighted baseball throwing program on pitch velocity, pitching arm biomechanics, passive range of motion, and injury rates

Key points

1. 01Pitch velocity rose about 3.3% (roughly 1 m/s) in the weighted-ball group, a statistically significant increase
2. 0224% of the weighted-ball group (4 of the training group) sustained elbow injuries, while no control pitchers were injured
3. 03The weighted-ball group gained 4.3 degrees of shoulder external rotation range of motion, a change linked to the velocity gain
4. 04This was a Level 1 randomized controlled trial in pitchers aged 13 to 18, but the sample was very small
5. 05Authors urge caution despite the velocity benefit because of the notable injury rate

How it was conducted

Design

Randomized controlled trial, Level 1 evidence

Participants

38 healthy baseball pitchers aged 13 to 18 years (mean 15.3 years)

Groups

Training group (n=19) doing a 6-week weighted-ball program 3 times per week with 2 to 32 ounce balls, vs control group (n=19) using only a 5-ounce regulation ball; both did strength training

Outcomes

Pitch velocity, shoulder and elbow passive range of motion, shoulder strength, elbow varus torque, arm angular velocity, and injury rates

Analysis

2-way repeated-measures ANOVA at P < 0.05; injuries tracked through training and the following season

What they found

• Training group pitch velocity rose from 29.9 +/- 1.5 to 30.9 +/- 1.5 m/s, a 1.0 m/s (3.3%) increase (post hoc P < 0.001; two-way P = 0.06)
• Dominant shoulder external rotation increased 4.3 degrees in the training group (post hoc P = 0.01; two-way P = 0.02), rising from 137.2 +/- 2.7 to 141.9 +/- 2.7 degrees
• No significant differences in elbow varus torque (training +2.3 N.m, P = 0.35) or arm angular velocity (training -111.6 deg/s, P = 0.37)
• 4 of the training group (24%) sustained elbow injuries: 2 olecranon stress fractures, 1 partial UCL injury, and 1 UCL injury needing surgical reconstruction (player retired); no control group injuries
• Control group showed a significant post hoc gain of 12.8 N in dominant shoulder external rotation strength (P = 0.003); two-way comparison not significant (P = 0.19)
• 80% of the training group increased pitch velocity and 12% decreased; 67% of the control group also increased

Limitations

• Very small sample size, with only 34 of 38 completing testing and 4 training-group dropouts
• Control group throwing was not directly supervised
• Restricted to ages 13 to 18, limiting generalizability to older or professional pitchers
• Short 6-week intervention with injury follow-up only through the subsequent season

Why it matters

For patients

If you are a young pitcher considering weighted-ball training to throw harder, weigh the modest velocity gain against a meaningful risk of elbow injury.

For clinicians

Counsel adolescent pitchers and families that weighted-ball programs can raise velocity but carry a notable injury risk and increase shoulder external rotation motion, so monitor arm health closely.

For readers

This Level 1 trial shows weighted-ball training is a trade-off, offering small velocity gains alongside a 24% injury rate in trained youth pitchers.